Internal electrode type plasma processing apparatus and plasma processing method

ABSTRACT

A plasma processing apparatus is of an internal electrode type, and an inductive coupling type electrode arranged facing a substrate has a shape formed by bending back a conductor at its central portion. A high frequency power is supplied to an end of the electrode so that a standing wave of half wavelength are produced at straight portions formed by bending back the electrode to make an antinode there and thus a plasma discharge is generated around the electrode. The controlled standing waves with its antinodes positively generated at the straight portions of the electrode are effectively used.

TECHNICAL FIELD

The present invention relates to an internal electrode type plasmaprocessing apparatus and plasma processing method, more particularly,relates to a plasma processing apparatus and plasma processing methodprovided with an inductive coupling type electrode suited for depositionof an amorphous silicon thin film used for solar cells or thin filmtransistors and the like on a large-area substrate.

BACKGROUND ART

The electrodes of internal electrode type plasma CVD apparatuses haveconventionally been of the parallel-plate type or the inductive couplingtype.

If using the parallel-plate type electrode, when trying to raisefrequency of a high frequency power in order to increase a filmdeposition rate and improve film characteristics, the problem arisesthat the electric discharge becomes non-uniform. This is caused by theoccurrence of a standing wave on the electrode plate resulting onnon-uniform distribution of plasma density and by the production ofplasma at undesirable locations due to the voltage created by thefeedback current to the ground. Further, as the substrate holder is madeto function as a ground electrode, the backing plate for the substratebecomes required and there is the difficulty of maintaining theclearance between the backing plate and substrate uniform when the sizeof the electrode plate is increased so as to form a film on a large-areasubstrate. Also, handling of the backing plate becomes difficultgenerally. Therefore, a parallel-plate type electrode is not well suitedto the deposition of a film on a large-area substrate.

As opposed to the above parallel-plate type electrode, an inductivecoupling type electrode is free from the above problems. Accordingly,the inductive coupling type electrode is well suited to the depositionof a film on a large-area substrate when used in an internal electrodetype plasma CVD apparatus, for example.

As an internal electrode type plasma CVD apparatus using an inductivecoupling type electrode, for depositing an amorphous silicon thin filmon a large-area substrate to form a solar cell etc, there is theapparatus disclosed in Japanese Unexamined Patent Publication (Kokai)No. 4-236781, for example. In this plasma CVD apparatus, the electrodefor discharge is formed by a flat coil having a ladder-like structurewhich is arranged parallel to the substrate. The ladder-like flat coilis formed by a conductive wire. The source gas is introduced from areaction gas introduction pipe provided at a single location of thereactor, while the inside of the reactor is evacuated through anevacuation pipe provided at a single location of the reactor. This flatcoil increases the intensity of the electromagnetic field and improvesthe uniformity of the field. Further, as a similar conventional plasmaCVD apparatus, there may be the apparatus disclosed in Japanese PatentNo. 2785442. In this plasma CVD apparatus, as the electrode arrangedfacing the substrate, a flat coil electrode formed by a singleconductive wire bent multiple times to form a zigzag configuration isused. A high frequency power is supplied from a high frequency generatorto the two ends of this electrode.

Concerning the above inductive coupling type electrode, theladder-shaped flat coil electrode according to Japanese UnexaminedPatent Publication (Kokai) No. 4-236781 does not have a uniform currentflowing at each rung of the ladder configuration and therefore does notgive a uniform distribution of the electromagnetic field, so has theproblem of the inability to deposit a uniform film on the large-areasubstrate.

The ladder-shaped flat coil electrode is a distributed constant circuitin view of an electric circuit. A current flowing at each section in thedistributed constant circuit can not be calculated simply fromresistance and path length of the circuit. In the ladder type electrode,an impedance of each ladder rung relative to other ladder rungs and ageometrical relation between each ladder rung and a feeding point isrelated to the magnitude of Poynting vector at each ladder rung.Experimentally, the phenomenon that most of the current flows at theladder rung near the feeding point is observed.

Further, since the zigzag flat coil electrode according to JapanesePatent No. 2785442 is produced by bending a single long conductive wireand the high frequency power is supplied from one end, the power cannotbe fed efficiently. Further, while effort is made in the design toprevent the generation of a standing wave as much as possible, it isimpossible to prevent the generation of a standing wave at undesirablelocations due to the configuration of the electrode. Therefore, the filmdeposition is disturbed. That is, an unintentional standing wave isproduced at the electrode, and this standing wave disturbs thedistribution of plasma and results in poor uniformity of filmdeposition.

Then, in the plasma CVD apparatus and the like of the internal electrodetype and inductive coupling type, it is desired to generate the plasmaaround the electrode by positively producing and utilizing the standingwave along the electrode arranged in the processing chamber. The plasmagenerated around the electrode receives energy for plasma generationfrom the antinode portion of the standing wave. Accordingly, it ispreferred to control the standing wave generated along the electrode andthe number or the positions of the antinodes to be formed in a desirablesituation. Thereby, the standing wave can be actively used in acontrollable state so that the antinodes are produced at desirablepositions along the electrode, and therefore it is possible toskillfully control a distribution of plasma and to deposit a film on alarge-area substrate with a good situation.

Further, as a general discussion, when proposing an electrodeconfiguration in the internal electrode type plasma processingapparatus, concerning the standing wave positively produced on theelectrode, the relationship between the frequency of the high frequencypower supplied to the electrode and plasma produced around the electrodein the reactor due to the high frequency power sometimes cannot beignored. Further, the plasma exited around the electrode due to thestanding wave formed on the electrode, specifically the plasmaparameters, have a major effect on the standing wave and sometimes makeit necessary to reevaluate the design parameters of the electrodeconfiguration. In this case, it is required that sufficientconsideration be given to the plasma parameters when designing theelectrode.

The objective of the present invention is to solve the above problems,positively utilize a standing wave in a controllable state to achieve agood uniformity of the plasma density, realize a configuration of theelectrode considering the plasma parameters around the electrode, and toprovide an internal electrode type plasma processing apparatus andplasma processing method which is suitable for deposition of a film on alarge-area substrate for a solar cell etc.

DISCLOSURE OF INVENTION

The internal electrode type plasma processing apparatus and methodaccording to the present invention are configured so as to achieve theabove objects.

The plasma processing apparatus of the present invention is theapparatus of the internal electrode type provided with an inductivecoupling type electrode arranged in a vacuum processing chamber. Theabove electrode is formed so that the total length thereof issubstantially equal to an excitation wavelength, and one end of theelectrode is grounded and another end is connected to a high frequencypower source. A standing wave of one wavelength is produced along theelectrode when the high frequency power source supplies a high frequencypower to the electrode. When producing the standing wave on theelectrode, a node of the standing wave along the electrode is formed ata central portion of the electrode, and antinodes of the standing waveare formed at half portions of said electrode, which exists at bothsides of a center point.

Each part of the standing wave, which are produced on the halves of theelectrode, are mutually intensified to supply the electromagnetic energyto the surrounding space of the electrode, and the plasma of uniformdensity is generated in the surrounding space of the electrode. Whengenerating the plasma within the processing chamber, active use of thestanding wave positively generated on the electrode is performed.

In the above plasma processing apparatus, the electrode is formed to beU-shaped by bending it back at the central portion, and each of the halfportions of the electrode corresponds to a straight portion, and bothhalf portions are arranged in parallel.

In the above plasma processing apparatus, the length of the half portionof the electrode is substantially equal to a half of the wavelength ofthe supplied high frequency power.

In the above plasma processing apparatus, a plurality of the electrodesare arranged to make a stratified structure comprising a plurality oflayers within the vacuum processing chamber, a plurality of filmdepositing regions are produced using the space between the electrodesincluded in the plurality of layers, and film deposition on a substrateis performed in each of the plurality of film depositing regions. Thisstructure can increase a processing efficiency of substrates.

The plasma processing apparatus of the present invention is theapparatus of an internal electrode type, which is provided with aninductive coupling type electrode in a vacuum processing chamber, andthe electrode is formed so that a total length of the electrode isdetermined to natural number times of a half of an excitationwavelength, one end of the electrode is grounded and another end thereofis connected to a high frequency power source, and standing waves areproduced along the electrode when the high frequency power sourcesupplies a high frequency power to the electrode, and further a node ofthe standing waves produced along the electrode is formed at a centralportion of the electrode, and at least one antinode of the standingwaves is formed at half portions of the electrode, which exist at bothsides of a center point.

In the above plasma processing apparatus, the electrode is formed to beU-shaped by bending it back at the central portion, and each of the halfportions of the electrode is a straight portion, both of the halfportions are arranged in parallel, and the node of the standing wave isconsistent with a bending back point.

In the above plasma processing apparatus, a plurality of electrodes arearranged to make a stratified structure comprising a plurality of layerswithin the vacuum processing chamber, a plurality of film depositingregions are produced using the space between the electrodes included inthe plurality of layers, and film deposition on a substrate is performedin each of the plurality of film depositing regions.

The plasma processing apparatus of the present invention comprises aplurality of electrodes of an inductive coupling type in a vacuumprocessing chamber, and each of the plurality of electrodes is formed bybending back a conductor at its central portion to be U-shaped, thestraight portions formed by the bending back are made parallel and arearranged to be in one plane, and further one end of each of theelectrodes is grounded and another end thereof is connected to a highfrequency power source. Further, the plurality of electrodes positionedparallel to each other are placed so that a straight portion of a powersupplying side is adjacent to a straight portion of a grounded side, andhigh frequency powers respectively supplied into the ends of thestraight portions of power supplying side for the plurality ofelectrodes are in phase.

In the above plasma processing apparatus, the length of each straightportion formed by bending back the plurality of electrodes is determinedto produce an antinode of a standing wave on the straight portion.

In the above plasma processing apparatus, plural electrodes arranged tobe in one plane is configured as an electrode array, a plurality of theelectrode arrays are placed as a stratified structure within the vacuumprocessing chamber, a plurality of film depositing regions are producedusing a space between said electrode arrays of plural layers, and filmdeposition on a substrate is performed in each of the plurality of filmdepositing regions.

The plasma processing apparatus of the present invention comprises anelectrode of an inductive coupling type in a vacuum processing chamberand the electrode is formed by bending back a conductor at its centralportion to be U-shaped. Further, a plasma discharge is produced aroundthe electrode by supplying a high frequency power to an end of theelectrode so that a standing wave of half wavelength is produced at astraight portion formed by bending back the electrode. In this case,frequency (f) of the high frequency power at this time is determined byf=(c/{square root over ( )}∈_(p))/2L1, where c is the speed of light, L1is the length of the straight portion formed by bending back theelectrode, and ∈_(p) is the relative dielectric constant of plasmaproduced around the electrode.

In the above plasma processing apparatus, the frequency of the highfrequency power is changed according to plasma parameters around theelectrode.

In the above plasma processing apparatus, a plasma CVD processing isperformed for depositing a film with a solar cell function on a largearea substrate within the vacuum processing chamber.

In the above plasma processing apparatus, the length L1 of the electrodeis preferred to be more than 0.8 meter.

The plasma processing method of the present invention is the processingmethod executed in the plasma processing apparatus having an electrodeof an inductive coupling type placed within a vacuum processing chamber,and the plasma processing method is characterized in that the electrodeis formed by bending back a conductor at its central portion, a totallength of the electrode is determined to be a natural number times of ahalf of an excitation wavelength, a high frequency power is supplied toend of the electrode, a node of a standing wave produced in theelectrode is consistent with a bending back point, and the standing wavemakes density distribution of plasma around the electrode to be uniform.

The plasma processing method of the present invention is the methodexecuted in a plasma processing apparatus comprising an electrode of aninductive coupling type in a vacuum processing chamber, and theelectrode is formed by bending back a conductor at its central portionto be U-shaped, and a plasma discharge is produced around the electrodeby supplying a high frequency power to an end of the electrode so that astanding wave of half wavelength is produced at a straight portionformed by bending back the electrode.

In the above plasma processing method, frequency (f) of the highfrequency power at this time is determined by f=(c/{square root over ()}∈_(p))/2L1, where c is the speed of light, L1 is the length of thestraight portion formed by bending back the electrode, and ∈_(p) is therelative dielectric constant of plasma produced around the electrode.

In the above plasma processing method, the frequency of the highfrequency power is changed according to plasma parameters around theelectrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of an electrode showing the internal structure ofa plasma processing apparatus according to a basic embodiment of thepresent invention.

FIG. 2 is a side view of the inside of the basic embodiment.

FIG. 3 is a front view of an electrode showing the internal structure ofanother embodiment of the present invention.

FIG. 4 is a front view of an electrode showing the internal structure ofanother embodiment of the present invention.

FIG. 5 is a side view of the inside of the above other embodiment.

FIG. 6 is a view of an example of the mechanism for conveying asubstrate.

FIG. 7 is a side view of the internal structure of another embodiment ofthe present invention.

FIG. 8 is a view of the electrode length in relation to a sinusoidalwaveform.

FIG. 9 is a view of the electrode half-length in relation to thesinusoidal waveform.

BEST MODE FOR CARRYING OUT THE INVENTION

The preferred embodiments of the present invention will be describednext with reference to the attached drawings.

The basic embodiment of the present invention will be explained firstwith reference to FIG. 1 and FIG. 2. The plasma processing apparatusaccording to this embodiment is, for example, an inductive coupling typeplasma CVD apparatus for depositing a thin film having the function of asolar cell on a substrate.

The film-deposition chamber 11 is a reactor in which a film is depositedor grown on a substrate conveyed inside by plasma CVD and is able to beset to required vacuum conditions. The film-deposition chamber 11 has asingle electrode 12 arranged in a vertical standing state, for example.The electrode 12 is supplied with high frequency power as explainedlater through its one end. This electrode 12 has the function of anantenna for supplying the high frequency electric power to thefilm-deposition chamber 11. The electrode 12 is preferably formed by aconductive wire (conductive line-shaped member), which has a requisitelength and diameter with relation to the frequency of the supplied highfrequency power, bent back at its central portion (bent back point) soas to be in one plane and thereby being given a substantially U-shapewhen seen from the front view. The electrode 12 has a bent back portionwith a curved shape and two straight portions to be substantiallyparallel.

In this embodiment, for example, the electrode 12 is arranged to bevertical with the curved bent portion at the top and the open ends atthe bottom. Note that it is also possible to arrange it with the curvedbent portion at the bottom and the open ends at the top. The structuresupporting the electrode is not illustrated, but any support structurecan be employed.

By bending the conductive wire into two, a U-shaped electrode 12 isformed, and the half length is shown by L3 in the figure as the lengthbetween the center point 12 a and the ends. The portion of the length L3is the length of a straight portion formed by bending back the electrode12 (hereinafter referred to as “the bent back straight portion”) and isthe portion in which the antinode of the standing wave is produced.

In the electrode 12, the high frequency power is supplied to the end 12b. A high frequency generator or power source 13 supplying the highfrequency power is provided at the outside of the film-depositionchamber 11. The feeder 14 from the high frequency generator 13 is ledthrough a connection part 15 provided at the film-deposition chamber 11into the inside of the film-deposition chamber 11 and connected to theend 12 b of the electrode 12. By this, the high frequency power issupplied w to the electrode 12. The connection part 15 has a built-infeed-through structure by which the feeder passes through the wall ofthe film-deposition chamber 11. The end 12 b of the electrode 12 servesas the feeding point.

The other end 12 c of the electrode 12 is electrically connected to thefilm-deposition chamber 11. The film-deposition chamber 11 is made of aconductive member (metal member) and is maintained at the groundpotential by being grounded. Therefore, the other end 12 c of theelectrode 12 is grounded. The other line 13 a of the high frequencygenerator 13 is grounded.

The two ends of the U-shaped electrode 12 are supplied by the highfrequency generator 13 with a high frequency power of a frequency higherthan the conventionally used high frequency power (for example, 13.56MHz). The high frequency power used here is a high frequency powerhaving the frequency of 60 MHz or more, for example. In the case of thepresent embodiment, however, the frequency of the high frequency powersupplied to the electrode 12 is determined by a specific method,explained later, in consideration of the plasma parameters around theelectrode 12.

A single backing plate 16 is, for example, arranged in a state parallelto the plane containing the electrode 12 at one side of the electrode12. Also, for example, four disk-shaped substrates 17 are arranged onthe surface of the backing plate 16 facing the electrode. The backingplate 16 has the function of a substrate holder with a built-in heater.Also, the four substrates 17 are arranged on the backing plate 16 alongthe longitudinal direction of the U-shaped electrode 12. As shown inFIG. 1, in this embodiment, the four substrates 17 are placed to existcorresponding to the position of the space between the two straightportions of the U-shaped electrode 12.

The plasma CVD apparatus according to the present embodiment uses theinductive coupling type electrode, so unlike a parallel plate typeelectrode, the above backing plate is not necessarily essential. Use ofthe backing plate is however preferable to improve the uniformity of thesubstrate temperature and to shield the heater panel from theelectromagnetic field. Note that in the plasma CVD apparatus shown inFIG. 1 and FIG. 2, for convenience in explanation, the illustrations ofthe source gas feed mechanism, the vacuum evacuation mechanism (vacuumpump), the substrate holder, the detailed structure of the substrateheating mechanism, the substrate cooling mechanism, etc. are omitted.

The conductive wire used for the electrode 12 is for example rod-shapedand is made from a metal material such as stainless steel or aluminum.When the electrode 12 is rod-shaped, its diameter is for example atleast 5 mm. In FIG. 1, the relationship between the length of thestraight portions L1 formed by bending back the conductive wire into twoand the width between the two bent back portions L2 is drawn with thelength L2 shown exaggerated larger than it actually is for conveniencein the explanation. As an actual preferable embodiment, L1 is forexample 75 cm to 2.0 m and L2 is for example about 8 cm. Therefore, thedegree of curvature of the upper bent portion of the actual electrode 12is also not as large as illustrated. In FIG. 1, as the lengths of thebent back portions of the electrode, the length L1 of the straightportion and the length L3 including half of the bent portion are shown,but the bent portion is considerably smaller than the straight portionsin length, so the length L1 and the length L3 may be considered to besubstantially the same in practice.

The length L1, in practice, is determined in accordance with the size ofthe substrate on which the film is to be deposited and is set as thelength necessary for generating a standing wave, so is determined by therelation with the frequency of the high frequency power supplied. Forexample, when the frequency is 120 MHz, L1 becomes 1.25 m.

In principle, the length L1 (or length L3) of the bent back straightportions in the electrode 12 is found by the relationship of

L1=c/2f=λ/2 (or f=c/2L1)  (1)

where f is the frequency of the high frequency power supplied, c is thespeed of light, and λ is the wavelength. According to this relationshipif the size (dimensions etc.) of the electrode is determined in relationto the substrate (glass etc.), the frequency of the high frequency powersupplied to the electrode is determined. Conversely, if the frequency ofthe high frequency power is determined, the dimensions etc. of theelectrode are determined.

According to the above relationship (1), L1 becomes substantially equalto half of the wavelength of the high frequency power, while the totallength L0 (=2L1) of the electrode 12 becomes substantially λ.

If the frequency becomes smaller than 120 MHz, the length L1 becomeslarger than 1.25 m and the electrode cannot be provided inside thefilm-deposition chamber 11 in some cases. In such a case, for example,it is possible to reduce the length L1 by adding a coaxial cablestructure to the ends of the electrode in order to provide a delayedwave structure relating to the electromagnetic wave. L1 is preferablyset to a range of 75 cm to 1.25 m by doing this as explained above. Thelengths L1 and L2 may be freely changed in accordance with theobjective.

According to the electrode 12 having the above shape, if a highfrequency power is supplied from the high frequency generator 13,standing waves with half of the wavelength can be formed at the straightportions formed by bending back the electrode, that is, the two straightportions having the length L1. The standing wave formed on the electrodeis controlled so as to produce the antinodes of the standing wave at thecentral part of each of the two straight portions and the node at thecenter point 12 a which is the bent back point.

In other words, the shape and dimensions of the electrode 12 is designedand the frequency of the high frequency power supplied to the electrode12 is determined so that the standing waves are positively createdhaving, for example, one antinode at each of the two parallel straightportions of the electrode 12. Further, when supplying the high frequencypower from the high frequency power generator 13 to the U-shapedelectrode 12, one end 12 b is made to be the feeding point and the otherend 12 c is connected to the ground. By doing this, the standing wave ofone wavelength is generated on the electrode 12 with controlled standingwaves generated at the two straight portions of the electrode 12. In thestanding waves of the half wavelength generated at each of the twostraight portions of the U-shaped electrode 12, their antinodes areconsistent in their positions and they mutually intensifies at theregion between the straight portions. As a result, plasma with a uniformdensity is generated in the region between the two straight portions ofthe electrode 12 and in the surrounding regions.

As explained above, by the film-deposition chamber 11 provided with theelectrode 12, when the inside of the film-deposition chamber 11 isevacuated to a required vacuum state by the vacuum pump, filled with asource gas etc. and a high frequency power of for example 100 MHz is fedthrough the end 12 b to the electrode 12, controlled standing waves areproduced at the two straight portions and plasma 18 having a uniformdensity is generated in the space surrounding the U-shaped electrode 12.A film is deposited on the four disk-shaped substrates 17 provided onthe backing plate 16 by the resultant plasma CVD action. The standingwave is formed at each of the halves of the electrode 12 from the centerpoint 12 a, that is, the above-mentioned two straight portions. Thestanding waves control the plasma 18 to achieve a good distribution ofthe plasma. In particular, as mentioned above, the electrode 12 isdesigned so that the standing waves with half wavelength produced at thetwo straight portions are strengthened, so there is no fall in thedensity of the plasma 18 produced in the space surrounding the electrode12 and the plasma 18 is controlled in state to the preferabledistribution of density.

Note that the number of the antinodes at each of the two bent backstraight portions of the electrode 12 is not necessarily limited to one.For example, it is possible to produce the standing waves having pluralantinodes by supplying the high frequency power with the frequencyhigher than 100 MHz to the electrode 12 with above-mentioned dimensions.In this case, the relationship between the total length of the electrode12 and the wavelength of the supplied high frequency power used for theexcitation, is maintained, so that the total length of the electrode isa natural number times of the half of the excitation wavelength, and anode is formed at the bent back point of the U-shaped electrode 12.

As the relationship between the total length of the electrode and thewavelength of the supplied high frequency, by selecting the wavelengthto form a standing wave at the bent back straight portions of theelectrode 12 as mentioned above, a strong electromagnetic field strengthcan be generated in the region surrounding the electrode functioning asthe antenna. If a discharge frequency becomes different from thedesigned one, a traveling wave from the feeding point of the electrodeand a reflecting wave returned from the grounding point cancel eachother on the electrode, and consequently effective electromagnetic fieldcan not be produced around the electrode. This matter can beexperimentally observed as a phenomenon that the electric discharge doesnot happen without giving the specific relationship between the lengthof the electrode (the length of the antenna) and the wavelength of theexcitation high frequency.

Especially, if the total length of the electrode is equal to onewavelength, the node is made at the feeding point, the bent back pointor the grounding point, and the electromagnetic field having thestrength not being zero is produced at the remaining portions.Therefore, by making use of the electromagnetic field not being zero,plasma is generated and uniform film deposition can be performed aroundthe center of the straight portions of the electrode.

Further, in the above structure, the bent portion of the U-shapedelectrode 12 does not have to be exactly a curved shape and it may bebent sharply or in an angled shape. Also, the two straight portions ofthe electrode 12 are unnecessary to be strictly parallel. The shape ofthe electrode may be of V-shaped, for example, instead of the U-shapedone.

Further, it is possible to make the electrode having a shape similar tothe U-shaped one as a whole by arranging the two different straightconductors in parallel and coupling the ends of them with anothercoupling member. That is, it is possible to form the electrode 12 bymaking the U-shape with the combination of some conductors.

Also, in the above structure, although the electrode 12 is placed in thevertical standing state to be toward a vertical direction, it may beplaced in a lateral state to be toward a horizontal direction. In thiscase, the backing plate and the substrate are also arranged in thelateral state of the horizontal direction.

According to the above embodiment, because an inductive coupling typeelectrode is used, there is the advantage that the plasma density caneasily be raised compared with a capacitive coupling type electrode.Further, by making the electrode U-shaped and using one of the ends ofthe electrode as the feeding point, due to the interaction of thestanding waves produced at the two bent back straight portions, theplasma is strengthened and the density of the plasma can be kept frombecoming nonuniform.

Further, according to the above embodiment, it is possible tomanufacture the electrode more inexpensively than a parallel plate typeelectrode and the electrode is suited to depositing a film on a largearea substrate.

When using a high frequency power of 100 MHz for example, the wavelengthλ of the high frequency power is 3 m. Therefore, the size of theelectrode 12 becomes about 150 cm (length)×12 cm (width), while the areaeffective for depositing a film becomes 120 cm×10 cm or so. In FIG. 1and the like, disk-shaped substrates were drawn as the objects on whichthe film is to be deposited, but the plasma CVD apparatus of the presentembodiment is more suited to depositing a film on rectangularsubstrates. Further, it is also suited to form films on not onlystationary objects, but also on large-area moving substrates. By the useof the above internal electrode type plasma CVD apparatus with highfrequency power, the ion bombardment on the depositing film is reduced,good film characteristics can be obtained, and a large area, highquality film can be formed.

Next, the practical conditions of the basic method of designing theinternal electrode explained above will be considered.

The following modifications may be considered in the electrode design(antenna design) in view of the practical conditions. If the highfrequency power is given from the high frequency generator 13 to theelectrode 12, an electric discharge occurs and plasma is produced aroundthe electrode 12 when an discharge gas is introduced into thefilm-deposition chamber 11 and the requisite vacuum state and otherconditions are met. If plasma is produced around the electrode 12, thevalue of the relative dielectric constant of the surrounding space asdetermined by the initial basic electrode design (relative dielectricconstant ∈_(r) at free space) becomes different. As a result, while astanding wave of half the wavelength was supposed to be produced at theportion of half the length of the electrode in relation with the lengthof the electrode, this design no longer holds true. Therefore, whendimensional conditions of the electrode 12 are given, the occurrence ofthe discharge around the electrode 12 after supplying the high frequencypower should be envisioned and the frequency of the high frequency powerdetermined envisioning plasma parameters.

If the discharge occurs around the electrode 12 and plasma is generated,the relative dielectric constant of the space around the electrode 12 isno longer 1. Therefore, the frequency of the high frequency powersupplied to the electrode 12 is determined in consideration of thedischarge conditions around the electrode 12. That is, if the relativedielectric constant of the plasma around the electrode 12 is ∈_(p), thefrequency f is determined by (c/{square root over ( )}∈_(p))/2L1 . . .(2). Note that the relative dielectric constant ∈_(p) is given by theformula: ∈_(p)=1−ω_(p) ²/ω(ω−jν) . . . (3). Here, ω_(p) is the plasmafrequency determined by the electron density, ω_(p) is the dischargefrequency, and ν is the collision cross section determined by thedischarge pressure. The ∈_(p) of the above formula (2) is the value ofthe real part of formula (2) and is not necessarily limited to 1 ormore.

Because the dielectric constant of the plasma differs depending on thedischarge conditions, the determination of the frequency is extremelydifficult. Therefore, in practice, the optimal discharge frequency isdetermined by experiments. Additionally, FIGS. 8 and 9 show theelectrode length L and half-length L/2 in relation to a sinusoidalwaveform E. In FIG. 8, the waveform E and the electrode begins at groundpotential, located at A to the beginning of the bent-back portion B ofthe electrode near the node. The waveform E continues to the end of thebent-back portion C to terminate at the power source located at D. Thus,the electrode extends from the ground to power source locations A to Dto length L. In FIG. 9, the length from A to B and from C to D extendsabout a half-length L/2, such that the distance from A to B and from Cto B is much greater than the distance from B to C.

Another embodiment of the present invention will be explained next withreference to FIG. 3. FIG. 3 is a view similar to the above-mentionedFIG. 1. In FIG. 3, elements substantially the same as elements explainedwith reference to FIG. 1 are assigned the same reference numerals. Inthis embodiment, an inductive coupling type plasma CVD apparatus of theinternal electrode type provided with electrodes having a configurationsuitable for depositing a film on a larger sized rectangular substrate21 is shown. The rectangular substrate 21 has a large area and ispreferably a glass substrate on which a film of amorphous silicon isdeposited for used as a solar cell. Plasma generating area is set over abroad area to face the film-deposition surface of this large arealarge-sized rectangular substrate 21, and therefore, the portionrelating to the electrode is provided with five electrodes which aresame as the above-mentioned U-shaped electrode 12. The five electrodes22A, 22B, 22C, 22D and 22E are arranged to be included in a single planeparallel to the film-deposition surface of the rectangular substrate 21,which is vertical for example, and are provided in a line so that theirstraight portions are parallel with each other and preferably at equalintervals. In the electrode unit comprised by the electrodes 22A to 22E,the electrodes are arranged with their bent portions at the top and theends at the bottom. Each of the electrodes 22A to 22E is secured to thebottom wall of the film-deposition chamber 11. One end of each of theelectrodes is provided with a connection portion 15, while the other endis connected to the film-deposition chamber 11 so as to be grounded.Further, the film-deposition chamber 11 shown in FIG. 3 is formed to belarger than the film-deposition chamber shown in FIG. 1 along with thelarger size of the rectangular substrate 21. Note that thefilm-deposition chamber 11 is grounded as explained before.

In the configuration shown in FIG. 3, the five electrodes 22A to 22E areseparately attached to the film-deposition chamber 11, but theelectrodes array is configured so that the standing waves are generatedat the two parallel straight portions of each of the electrodes asmentioned above.

Each of the five electrodes 22A to 22E is supplied through itsconnection portion 15 with the high frequency power having apredetermined frequency from the single high frequency generator 13provided at the outside of the film-deposition chamber 11 keeping thesame phase relationship. The method of determination of the frequency ofthe high frequency power supplied is as explained in the previousembodiment, and the frequency is determined in consideration of thedischarge conditions. The high frequency power supplied from the highfrequency power generator 13 to each of the electrodes 22A to 22E is setso that the controlled standing waves are produced at the straightportions of each of the electrodes.

The standing waves produced at the straight portions of the electrodes22A to 22E are, as explained above, is controlled so that the plasmadensity of the space around the electrodes become uniform.

The above technical contents will be explained concretely. In FIG. 3,the electrode 22C is paid attention. In the electrode array, thepower-supplied side of the straight portion of the electrode 22C isadjacent to the grounded side of the straight portion of the electrode22B at the left side, and the grounded side of the straight portion ofthe electrode 22C is adjacent to the power-supplied side of the straightportion of the electrode 22D at right side. Watching only the electrode22C, the vectors' direction of the electromagnetic field is reversed ina phase aspect between the power-supplied and the grounded straightportions in the electrode 22C. The electromagnetic field in the regionbetween the power-supplied and the grounded straight portions in theelectrode 22C is made stronger in its density by mutual action, As tothe outsides of the power-supplied and the grounded straight portions ofthe electrode 22C, based on the relationship of the adjacent electrodes22B and 22D and the supply of the high frequency power to the electrodes22B and 22D, whose phase is identical to that of the high frequencypower supplied to the electrode 22C, the same relationship ofstrengthening the electromagnetic field is also made in the respectiveregions between the power-supplied side straight portion of theelectrode 22C and the grounded side straight portion of the electrode22B, and between the grounded side straight portion of the electrode 22Cand the power-supplied side straight portion of the electrode 22D.Thereby, the plasma of uniform density is generated in each of thoseregions. The above-mentioned characteristics are realized in the everyone of electrodes 22A to 22E.

Therefore, in the space in front of the film-deposition surface of therectangular substrate 21, no unevenness of intensity of theelectromagnetic field is produced, plasma is generated with a uniformdistribution of density, and a film of a uniform thickness is depositedon the large-area rectangular substrate 21. By controlling the standingwaves generated at the electrodes to the desired states as mentionedabove, the uniformity of film thickness can be improved.

In the above embodiment, the number of electrodes may be freely set inaccordance with the size of the substrate on which the film is beingdeposited. Further, while use of a single high frequency generator ispreferable, plural generators may also be used.

Next, further, another embodiment of the present invention will beexplained with reference to FIG. 4 and FIG. 5. In these figures,elements substantially the same as elements explained with reference tothe previous embodiments are assigned the same reference numerals. Inthis embodiment, three-layered electrode arrays 33, 34 and 35, eachcomprised of three electrodes 32A, 32B and 32C, are provided in astratified configuration at predetermined intervals from each other. Theindividual electrodes 32A to 32C are configured in the same way as theelectrode 12 explained in the above-mentioned basic embodiment. In eachof the three-layered electrode arrays 33 to 35, the electrodes 32A to32C are arranged to be contained at equal intervals in the same verticalplane. Further, the three electrode arrays 33 to 35 are arranged so thatthe planes they form are parallel. Rectangular substrates 31 arearranged at the two sides of each of the electrode arrays 33 to 35 sothat their film-deposition surfaces are parallel to the planes formed bythe electrode arrays. The rectangular substrates 31 are here glasssubstrates. Further, as shown in FIG. 5, heaters 36 are arranged at theoutside of the outermost rectangular substrates in the film-depositionchamber 11. The heaters 36 hold the rectangular substrates 31 at apredetermined temperature. The film-deposition chamber 11 is grounded.

In the above, each of the electrodes 32A to 32C of the electrode arrays33 to 35 is supplied with the high frequency power from the single highfrequency generator through the connection portion 15. The frequency ofthe high frequency power supplied to each electrode is, in the same wayas explained in the above embodiments, determined considering the plasmaparameters around the electrodes. As explained above, the controlledstanding waves are produced at each of the electrodes 32A to 32C of theelectrode arrays 33 to 35. Uniform plasma is produced at the two sidesof each of the electrodes 32A to 32C of the electrode arrays 33 to 35when the film-deposition chamber 11 is held in the required vacuum stateand source gas etc. is introduced. A film is deposited on thefilm-deposition surfaces of the six rectangular substrates 31 based onthe plasma CVD action using the high frequency power (for example, RF).Further, in the configuration of this embodiment, since the electrodesare inductive coupling types, no backing plates are required for holdingthe rectangular substrates 31 at the ground potential. The same is trueof the case of the embodiment of the configuration shown in FIG. 3. InFIG. 4 and FIG. 5, only the substrates 31 were shown, but in practicethe substrates 31 are held by support frames. The support frames havewindow-frame shaped structures.

FIG. 6 shows a window-frame shaped support frame 37 that sets andsupports two substrates 31. A substrate conveying mechanism 38 isprovided at the bottom of the support frame 37 and is designed to movethe substrates 31 on a guide path. The substrates 31 are conveyed in adirection vertical to the paper surface in FIG. 5 or FIG. 6.

Since the U-shaped electrode is shaped with the feeding end and groundend positioned in the same plane and a plurality of U-shaped electrodescan be arranged so as to be in the same plane as well, a multi-region(or zone) deposition device can be easily realized by utilizing alayered or stratified structure of electrodes arranged at predeterminedintervals as shown in FIG. 5. By enabling the multi-region filmdeposition in this way, films can be formed on a plurality of substratessimultaneously and the throughput of film deposition can be improved. Ifutilizing the layered structure, further, the ratio of the surface areaof the film-deposition surfaces of the rectangular substrates to thevolume inside the film-deposition chamber becomes larger, so escape ofheat can be suppressed and the power consumption can be suppressed.

Further, according to the above embodiment, since the backing plates ofthe substrates on which films are to be deposited can be omitted, thecost of the power used for raising the temperature of the backingplates, the cost of the cooling water required for cooling the backingplates, the running costs required for handling the backing plates, thehardware costs due to the load on the conveyance mechanism, and othercosts conventionally required can be eliminated. Further, theconventional system provided with backing plates suffered from theproblem of lack of uniformity of film thickness or poor filmcharacteristics due to the uneven degree of contact between the backingplates and substrates, but this problem is eliminated.

FIG. 7 shows another embodiment of the present invention. In thisembodiment, a structure is shown where the U-shaped electrodes of thepresent invention are provided in the plasma CVD apparatus of the typeusing substrate carriers for conveyance. The part of the structurerelating to the U-shaped electrodes is substantially the same as thestructure shown in FIG. 5. Therefore, in FIG. 7, elements substantiallythe same as the elements shown in FIG. 5 are assigned the same referencenumerals. In this embodiment, a substrate conveyance mechanism 42provided with a substrate support mechanism 41 is provided at the bottomof the film-deposition chamber 11. Therefore, electrode arrays 33 to 35having the above three-layered structure are arranged attached to thetop wall of the film-deposition chamber 11 and hanging down verticallyin the film-deposition chamber 11. The rest of the structure is the sameas that explained in FIG. 5. The plurality of substrates 31 supported bythe substrate support mechanism 41 are conveyed in a direction verticalto the paper surface in FIG. 7 by the substrate conveyance mechanism 42after the films are finished being formed on them.

In this embodiment as well, it is possible to form a film simultaneouslyon a plurality of substrates by multi-region deposition and there is noneed to provide the backing plates for the substrates on which the filmsare to be formed, so the effects explained with respect to the aboveembodiments are also exhibited.

In the above-mentioned embodiments, the bent portions and ends of theelectrodes may be provided with covers formed by a dielectric(insulator) to cover them. The covers function as electromagneticshields blocking the electromagnetic field from the electrode. Thecovers may also be given the function of elements for adjusting theimpedance of the electrode. The covers may for example be given acoaxial cable structure.

In the above-mentioned embodiments, the total length of the U-shapedelectrode was set to be equal to the excitation wavelength (λ), but asimilar action can be obtained by an electrode having a general bentback shape where the total length of the electrode is made naturalnumber (a whole) times of a half of the excitation wavelength of thehigh frequency power supplied if in this case supplying a high frequencypower from the end of the electrode and making the node of the standingwave produced at the electrode match with the bent back point of theelectrode.

While the invention has been described with reference to specificembodiment chosen for purpose of illustration, it should be apparentthat numerous modifications could be made thereto by those skilled inthe art without departing from the basic concept and scope of theinvention.

INDUSTRIAL APPLICABILITY

As mentioned above, the internal electrode type plasma processingapparatus and method according to the present invention is suited todeposit the film onto the large area substrate, and is useful of makingthe solar cells by depositing the amorphous silicon thin film on thelarge substrates, for example.

What is claimed is:
 1. In a plasma processing apparatus provided with an inductive coupled electrode for generating plasma in a vacuum processing chamber, the plasma processing apparatus wherein: said electrode is formed so that total length thereof is substantially equal to a wavelength of a supplied high frequency power, and is formed so that; one end of said electrode is grounded and another end thereof is connected to a high frequency power source for supplying said high frequency power, and a standing wave of one wavelength is produced along said electrode when said high frequency power source supplies said high frequency power to said electrode; and a node of said standing wave produced along said electrode is formed at a central portion of said electrode, and an antinode of said standing wave is formed on both portions respectively corresponding to a half portion of said electrode, which exist at both sides of said center point, wherein said electrode is formed to be U-shaped by having a bent-back portion at said central portion, each of the half portions of said electrode corresponds to a straight portion, both of the half portions are arranged in parallel, and a length of the half portion of said electrode is substantially equal to a half of the wavelength of said high frequency power, and the length of the half portion of said electrode is about one order of magnitude longer than a width between the half portions.
 2. A plasma processing apparatus as set forth in claim 1, wherein a plurality of said electrodes are arranged to make a stratified structure comprising a plurality of layers within said vacuum processing chamber, a plurality of film depositing regions are produced using a space between said electrodes included in said plurality of layers, and film deposition on a substrate is performed in each of said plurality of film depositing regions.
 3. In a plasma processing apparatus provided with an inductive coupled electrode for generating plasma in a vacuum processing chamber, the plasma processing apparatus wherein: said electrode is formed so that total length is determined to natural number times of a half of a wavelength of a supplied high frequency power, and is formed so that; one end of said electrode is grounded and another end thereof is connected to a high frequency power source for supplying said high frequency power, and standing waves are produced along said electrode when said high frequency power source supplies said high frequency to said electrode; and a node of said standing waves produced along said electrode is formed at a central portion of said electrode, and at least one antinode of said standing waves is formed on both portions respectively corresponding to a half portion of said electrode, which existing at both sides of said center point, wherein said electrode is formed to be U-shaped by having a bent-back portion at said central portion, each of the half portions of said electrode is a straight portion, both of the half portions are arranged in parallel, said node of said standing wave is consistent with a bending back point, and the lenth of the half portion of said electrode is about one order of magnitude longer than a width between the half portions.
 4. A plasma processing apparatus as set forth in claim 3, wherein a plurality of said electrodes are arranged to make a stratified structure comprising a plurality of layers within said vacuum processing chamber, a plurality of film depositing regions are produced using a space between said electrodes included in said plurality of layers, and film deposition on a substrate is performed in each of said plurality of film depositing regions.
 5. In a plasma processing apparatus provided with an inductive coupled electrode for generating plasma in a vacuum processing chamber, the plasma processing apparatus, wherein: total length of said electrode is substantially equal to a wavelength of a supplied high frequency power; one end of said electrode is grounded and another end is connected to a high frequency power source; said electrode is formed to be U-shaped so that a central portion of the total length thereof is a bent-back portion, with about half-portions on either side of said bent-back portion; each of the about half-portions of said electrode is a straight portion; the length of each straight portion is substantially equal to a half of the wavelength of the high frequency power supplied to said electrode; the straight portions are arranged in parallel; and the length of the about half-portions of said electrode is about one order of magnitude longer than the bent-back portion.
 6. A plasma processing apparatus according to claim 5, wherein the length of said electrode is a natural number times a half of the wavelength of the supplied frequency power. 